amd-xgbe: Perform phy connect/disconnect at dev open/stop

A change added to the mdiobus/phy api added a module_get/module_put
during phy connect/disconnect processing. Currently, the driver
performs a phy connect during module probe and a phy disconnect during
module remove. With the addition of the module_get during phy connect
the amd-xgbe module use count is incremented and can no longer be
unloaded.

Move the phy connect/disconnect from the driver probe/remove functions
to the net_device_ops ndo_open/ndo_stop functions.  This allows the
module use count to be decremented when the device(s) are brought down
and allows the module to be unloaded.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>